The present invention relates to a process for the preparation of 2-(aminodithio)thiazoles and 2-(aminotrithio)thiazoles by reacting a cyclic secondary amine, a 2-mercaptothiazole and sulphur in an inert organic solvent in the presence of an oxidant.
A typical representative of the compounds from the group of 2-aminodithiothiazoles is 2-(4-morpholinodithio)benzothiazole, which is used in large amounts as a vulcanization accelerator and sulphur donor. Processes for the preparation of 2-(4-morpholinodithio)benzothiazole have previously been described. They can be grouped as follows, depending on the starting compounds employed in each case: from morpholine sulphides and 2-mercaptobenzothiazole or dibenzothiazolyl 2,2'-disulphide (U.S. Pat. No. 3,489,754), from 2-mercaptobenzothiazole or dibenzothiazolyl 2,2'-disulphide, 4-morpholine and disulphur dichloride (U.S. Pat. No. 3,070,593), from 2-mercaptobenzothiazole, 4-morpholine, chlorine and disulphur dichloride (U.S. Pat. No. 2,983,726), from 2-mercaptobenzothiazole or dibenzothiazolyl 2,2'-disulphide, 4-morpholine, sulphur and oxidants such as sodium hypochlorite (DE-A 2,238,516), from morpholino-benzothiazole and sulphur (DE-A 1,134,677), and from sulphenamides, 4-morpholine and sulphur (U.S. Pat. No. 3,969,350). From amongst these, processes which are suitable for industrial realization are those which are based on the raw materials 2-mercaptobenzothiazole, 4-morpholine and sulphur, which are inexpensive and readily available, described in DE-A 2,238,516 and also in DE-A 2,164,480 and U.S. Pat. No. 3,281,418. According to the contents of these three publications, it is still necessary to employ expensive oxidants in a high stoichiometric excess, in particular those which are substantially soluble in water, in order to use them in aqueous solution. For example, ammonium peroxydisulphate or potassium peroxydisulphate, hydrogen peroxide, potassium permanganate and sodium hypochlorite or calcium hypochlorite are to be used, with sodium hypochlorite being preferred in all cases. The shortcoming encountered when most of these oxidants are used is that inorganic salts are formed as a by-product, for example sodium chloride in the case of the preferred sodium hydrochlorite, which contaminate the waste water or have to be removed. In these processes too, not only the oxidant but also the remaining reactants must be employed in high stoichiometric excesses.
A suggestion as to how the process for the preparation of 2-(4-morpholinodithio)benzothiazole from 2-mercaptobenzothiazole, 4-morpholine, sulphur and oxidant can be made more economical can be found in the above-mentioned publication DE-A 2,238,516. According to this publication, the 2-mercaptobenzothiazole is to be employed directly in the state in which it is obtained from the preparation of 2-mercaptobenzothiazole, i.e., water-moist and the drying step of the latter is thereby dispensed with.